Surge current instrument



p F. B. MENGER SURGE CURRENT INSTRUMENT Original Filed March 18, 1955 a9 1 v m w w nB at WAS A m 5 G 1. U P b Patented Sept. 25, 1934 IE-STATES PATENT ICE SURGE CURRENT INSTRUMENT Francis B. Menger,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York 4 Claims.

This application relates to surge current instruments and is-a divisionof my copending application Serial No. 661,550, filed March 18, 1933,and assigned to the assignee of this application.

5 In my copencling application there is disclosed a novel form of surgecurrent indicator for indicating whether or not a surge current haspassed through a conductor and the direction in which the surge currentpassed through the conductor,

and there is also disclosed a novel form of surge current measuringinstrument for measuring the maximum value of a surge current thatpassed through a conductor. The invention to be claimed in my copendingapplication will relate to the surge current indicator, whereas theinvention to be described and claimed in this divisional case willrelate to the surge current measuring instrument.

In electrical installations it frequently occurs that an electriccurrent surge fiows through'a conducting body for a very short period,and it is desired to have some instrument that will indicate this i acttogether with the direction in which the surge current flowed, theindication to remain visible after the occurrence of thesurge.

There is also a long-felt need in the'electrical industry for a simpleand inexpensive instrument that will accurately measure the maximumvalue of an electric current surge that flowed through a conductingbody, even though the surge lasts only a few micro-seconds. For example,there is an important need for an instrument that will accuratelymeasure the maximum value of the current surge that flows through atransmission tower arm supporting the line insulators when the latterare flashed over by reason of a lightning stroke, or by reason of aswitching operation and that will accurately measure the maximum valueof the surge current that flows through a lightning arrester due toeither of the above mentioned reasons. This information is of vitalimportance in lightning research and transmission system stabilityinvestigations, because it is a useful guide in determining what stepsshould be taken to decrease the number of trip-outs on a transmissionsystem.

Various attempts have been made to measure the maximum value of thesesurge currents. For example, the latest practice was to utilize thevoltagedrop caused by the surge current flowing in the tower armor leg,or in the lightning arrester ground lead, and to measure this voltagedrop by means of a Lichtenberg figure camera, such as shown, forexample, in United States Patent No. 1,649,180, Peters. The limitedvoltage sensitivity of this recorder made it necessary to bridge aconsiderable portion of the tower arm or leg, or lightning arresterground lead, in order to obtain a sufficiently high voltage to operatethe recorder, The effective resistance of the bridged portion wasuncertain because of skin effect phenomena, and in addition theinductive voltage drop could not properly be taken into account. In viewof these uncertain factors the measurement obtained of the surge currentwas unreliable. It therefore became desirable to provide an instrumentthat would accurately measure the maximum value of a surge currentpassing through a conducting body, irrespective of the duration of thesurge.

My invention provides an instrument that will indicate whether ornot asurge current has flowed through a conducting body, and that also willindicate the direction in which the surge current flowed. My instrumentwill also measure the maximum value of the surge current, irrespectiveof the-direction in which it flowed through the conductingbody. Brieflydescribed, my instrument comprises three strips of magnetic mate--rial;two of these strips being initially magnetized,

and the third strip possessing a high degree of magnetic retentivity andbeing initially unmagnetized, these strips being adapted to be sopositioned adjacent the conducting body that the magnetic 'fluxsurrounding the latter during a current surge therethrough in a givendirection passes through the strips in such a direction as to decreasethe magnetic strength of one of the initially magnetized strips and toincrease the magnetic strength of the other initially magnetized strip,and to magnetize the initially unmagnetized strip. Each initiallymagnetized strip has a movable magnetic armature which is normally heldin an attracted position by the magnetic force of its strip and whichis. biased to move to another position in response to a predetermineddecrease in the magnetic strength of its strip. Consequently, a currentsurge passing through the conducting body in one direction releases onearmature so that it moves to its other position, and a current surgepassing through the conducting body in the opposite direction releasesthe other armature so that it moves to its other position, thus not onlyindicating that a surge current has flowed through the conducting body,but also indicating the direction in which the surge current flowed. Theinitially unmagnetized strip also has a magnetic armature movable fromone to the other of two positions, one of these positions being itsattracted position when the strip is magnetized, the armature beingbiased to move to its other position. After a surge current has flowedthrough the conducting body in either direction, the initiallyunmagnetized strip becomes suiiiciently magnetized so that its magneticforce is capable ofv holding its armature in the attracted position.This magnetic force is substantially directly proportional to themaximum value of the surge current. The instrument also comprises meansfor exerting on this armature an opposing force of sufficient magnitudeto overcome the magnetic force of the strip holding the armature againstits ends, and means for indicating in terms of surge current themagnitude of the opposing force exerted on the armature.

My invention, however, will be best understood from the followingdescription when considered in connection with the accompanying drawing,while those features of my invention which are believed to be novel andpatentable are pointed out in the appended claims.

Fig. 1 represents a perspective View of a preferred form of myinstrument, part of the casing and cover being broken away to show theinternal parts. of the'instrument with its casing and cover unbroken,and showing the instrument connected up with some conducting body, andalso showing how it indicates that a current surge has'fiowed throughthe conducting body. Similar parts in both figures are represented bythe same reference numerals.

Referring to both figures, 10 represents a casing which is preferablymoulded out of insulating material and to which is removably secured byany suitable means (not shown) a cover '11 also preferably made ofinsulating material. The casing and cover are shown partly broken awayin Fig. 1 in order to illustrate the mechanism inside of the casing, butare completely shown in Fig. 2. Inside of casing 10 and projecting fromone of its walls are three substantially parallel plates 12, 13 and 14,these plates being integral with the casing and made out of the samematerial. The structures of these plates are identical, hence thestructure of only one of them, for example 12, will be described. Plate12 has'a filler-piece 15 separated therefrom by .1 a narrow horse-shoeshaped slot, the filler piece being preferably made of the same materialas the plate and casing. The arrangement is such that by inserting intothe slot a strip of material whose thickness is equal to the width ofthe slot, the plate, filler-piece and strip are held together as aunitary structure. The filler pieces for plates 13 and 1 1 are alsorepresented by 15. In the slot between plate 12 and its filler-piece isinserted a thin strip 16 of magnetic material possessing a high degreeof magnetic retentivity, as, for example, cobalt steel. The length ofstrip 16 is such that it will have two spaced apart ends projectingslightly beyond the vertical edges of plate 12 and its filler-piece. Inthe slot be-- tween plate 13 and its filler-piece is inserted a thinmagnet 1'1, preferably a permanent magnet, the length of the magnetbeing such that it will have two spaced apart ends projecting slightlybeyond the vertical edges of the plate and its filler-piece; A similarmagnet 18 is similarly placed in the slot between plate 14 and itsfillerpiece. Magnets 17 and 18 are positioned so that their magneticpoles are oppositely related. Thus, for example, magnet 17 is positionedso that its N pole is at the top and its S pole is at the Fig. 2represents a perspective view' bottom, whereas magnet 18 is sopositioned that its S pole is at the top and its N pole is at thebottom.

Plate 12 and its filler-piece are suitably notched near the center ofstrip 16 so that a coil 19 may be positioned to surround the centerportion of the strip in such a manner that the energization of the coilwill effect the magnetization of the strip. Coil 19 is first placed inthe notches of plate 12 and its filler-piece, and since strip 16 isflexible it is passed through the coil and then inserted in the slotbetween the plate and its fillerpiece. Similar coils 20 and 21 aresimilarly placed to surround portions of magnets 1'7 and 18,respectively. The ends of coils 19, 20 and 21 are connected to the pairsof binding posts 22, 23 and 2 1, respectively, secured to casing 10.Casing 10 and filler-pieces 15 are provided with aligned holes suitablypositioned so that the conductor through which the surge current mayflow can be passed through the holes insuch a manner that strip 16 andmagnets 17 and 18 will almost surround the conductor with the planes ofthe strip and the magnets substantially perpendicular to the axis of theconductor. This conductor may or may not form a part of the instrumentproper. For the sake of illustration, I have representedthis'conductorby numeral 25, and have shown it suitably secured tocasing 10 by bolt and washer means 26. In Fig. 2, I have shown thisconductor connected in series with a lead 27 through which a surgecurrent may flow.

Inside of casing 10 and secured to its baseis a three-arm bracket 28 onwhich is pivotally mounted a thin magnetic armature 29. This ar matureis preferably non-polarized and is preferably made of a materialpossessing a very low degree of magnetic rentivity. Bracket 28 andarmature 29 are so arranged that the armature can simultaneously engageboth projecting ends of strip-16 and can move toward and from theseends. A stop 30 secured to bracket 28 is preferably provided againstwhich armature 29 rests when it has moved to its farthest position awayfrom the ends of strip 16. Armature 29 is biased to movetoward stop 30,by means of a spiral spring'31 having one end thereof secured to thepivoted shaft'fastened to the armature and having the other end thereofsecured to an adjustable arm 32. Arm 32 is rotatably mounted in an armof bracket 28, and an axial extension from arm 32 projects through thecasing. To this extension is secured a knob 33 and a pointer 34, thelatter cooperating with a graduated scale 35 secured to the casing.

Inside of casing 10 and secured to its base are two brackets 36 and 37respectively. Pivoteol in bracket 36 is a thin-magnetic armature 38 sothat it can simultaneously engage both projecting ends of'magnet 17 andcan move toward and from these ends. This armature is biased to moveaway from the ends of magnet 1'7 by means of a spiral spring 39 havingone end thereof secured to the pivoted shaft fastened to the armatureand having the other end thereof secured to an adjustable arm 10.Pivoted in bracket 37 is a thin magnetic armature 41 so that it cansimultaneously engage both projecting ends of magnet 18 and can movetoward and from these ends. This armature is biased to move away fromthe ends of magnet 18 by means of a spiral spring 42 having one endthereof secured to the pivoted shaft fastened to the armature and theother end thereof secured to an adjustable arm 43. Annatures 38 and 41are preferably non-polarized, and,

are preferably made of a material possessing a very low degree ofmagnetic'retentivity. Cover 11 has slots 44 and 45, which are in thepath of movement of armatures 38 and 41 respectively. Neither ofarmatures 38 and 41 has any part thereof projecting through itsrespective slot in cover 11 when it engages both ends .of its respectivemagnet. However, when either armature moves away from the ends of itsrespective magnet, it falls through its slotin cover 11 and asubstantial portion of the armature projects through the slot, as shownfor example in Fig. 2 by the projection of-a substantial portion ofarmature 38 through slot 44. "Cover 11 also has a window 46 positionedabove armature 29 so as to render the latter and the projecting ends ofstrip 16 visible from the top of the cover.

A description of the operation follows: Arms 40 and 43 are so adjustedthat armatures 38 and 41 are biased to move away from the projectingends of magnets 1'7 and 18, respectively, with a biasing force on eacharmature slightly less than the magnetic force of its magnet, and,therefore, each armature is normally held in engagement with both endsof its magnet by the magnetic force of its magnet. Now assume thatacurrent surge passes through lead 27 in such a direction'as to flowthrough conductor 25 from its right-hand end to its left-hand end. Someof the magnetic flux surrounding the conductor 25 during the currentsurge therethrough will pass through strip 16 and magnets 17 and 18. Thedirection of this flux will be such as to strengthen magnet 18 andweaken magnet 1'7, hence armature 41 will remain in engagement with bothends of magnet 18, whereas the decreased magnetic strength of magnet 1'7will be insufficient to hold armature 38 against the biasing force ofspring 39, and, therefore, armature 38 will drop down through slot 44,as shown in Fig. 2, thus clearly indicating that a current surge haspassed through conductor 25. It is clear that if the current surge hadflowed in the opposite direction through conductor 25, then magnet 17would have been strengthened and magnet 18 would have been weakened,hence armature 38 would have remained in engagement with both ends ofits magnet 1'7 and armature 41 would have dropped down through slot 45.When the operator sees armature 38 projecting through slot 44-he knowsthat a surge current has passed through conductor 25 in a certaindirection, whereas if he sees armature 41 projecting through slot 45 heknows that a surge current has passed through conductor 25 in theopposite direction. If desired, arrows 47 and 48 may be secured adjacentto slots 44 and 45, respectively, as shown, to indicate the direction inwhich the surge current passed through the conductor. The properpositioning of these arrows may be determined by sending a surge currentthrough conductor 25 in a known direction and then securing an arrowpointing in the same direction adjacent the slot through which droppedeither one of armatures 38 or 41 in response to this surge, and thensecuring the other arrow pointing in the opposite direction adjacent theother slot. Each of armatures 38 and 41 is preferably made to be fairlylight so as to have a low moment of inertia about its pivotal axis, and,therefore, be responsive to slow, medium, and fast surges. To the sameend, magnets 1'? and 18 are preferably made of thin material. so as toreduce as much as is practically possible the eddy currents flowing inthem when they are traversed by the magnetic flux surrounding conductor25 during a current surge.

When a current surge flows through conductor 25 in either direction,some of the magnetic flux surrounding the conductor during the surgepasses through strip 16 and magnetizes it. The magnetic flux retained bystrip 16 after the surge is over depends on several factors, among whichare the thickness of the strip, its distance from conductor 25, themagnetic characteristics of the strip, the maximum value of'the surgecurrent, and the time it takes the surge current toreach its maximumvalue from zero. During the surge, the strip is threaded by a magneticflux of varying intensity surrounding conductor 25, hence eddy currentsare caused toflow in the strip, which tends to oppose the magnetizationthereof by'this flux. By making strip 16 of some material having a highdegree of magnetic retentivity, as, for example, cobalt steel, and bymaking'the strip of thin material, as, for example, .005' thick, thestrip will retain sufficient magnetic flux to give satisfactorymeasuring operation even after a very fast surge, as, for example, a 5micro-second surge. Furthermore, the value of the magnetic flux retainedby the strip at the end of the surge will then be substantially equal tothat which the strip would retain if a steady, direct current of thesame magnitude as the maximum value of the surge were passed throughconductor 25. Since with a given maximum value of surge current, theslower the surge the lower are the eddy currents that are caused to flowin strip 16, it follows that with slower surges than a 5 micro-secondthe magnetic flux retained by the strip will also be substantially equalto that which the strip would retain if a steady, direct current of thesame magnitude as the maximum value of the surge were passed throughconductor 25'. It therefore follows that by suitably selecting thethickness of strip 16 it is readily possible to have the magnetic fluxretained by itafter a surge be substantially directly proportional tothe maximum value of the surgecurrent, and be substantially independentof the duration of the surge from the slowest surge down to and including the fastest surge it is expected to measure.

When the operator sees that neither armature 38 nor 41 projects throughcasing 10, he knows that no surge current has passed through conductor25. However, when he sees one of these armatures projecting through thecasing, he knows that a current surge has passed through the conductor.He then goes over to the instrument to measure the maximum value of thesurge current. The magnetic flux retained by strip 16 after a surge mayor may not be enough to draw armature 29 into engagement with its ends.In either case the operator turns knob 33 anti-clockwise so as to makecertain that armature 29 is brought into engagement with both ends ofmagnetized strip 16. The operator then slowly turns the knob clockwiseuntil the force exerted by spring 31 on armature 29 is just sufficientto overcome the magnetic force of strip 16 holding the armature againstits ends, and the armature then drops away from the ends of the strip,the operator becoming aware of this fact either by viewing the armatureand the projecting ends of strip 16 through window 46 or by hearing thesound of the armature strike against stop 30. The operator then readsthe maximum value of the surge current from the GUI position ofpointer34 on scale 35, this scale being calibrated as described below.

After each surge, the operator, after measuring the maximum value of thesurge current, demagnetizes strip 16 and magnets 17 and 18, and thenremagnetizes magnets 17 and 18 so that they will have their originalmagnetic strengths with their original magnetic polarities, and thenpushes whichever armature is projecting through the casing back into itsplace against the ends of its magnet. This demagnetization may beeffected in any manner, as, for example, by connecting a magneto toterminals 22 and rotating the magneto armature at a continuallydecreasing speed until it is stopped altogether, and then doing the samewith-respect to terminals 23 and 24. The remagnetization may be effectedin any manner, as, for example, by connecting one or more dry cells toterminals 23 and sending a predetermined value of current flow throughcoil 20 for a minute or so in such a direction that magnet 17 will havethe relative positions of its poles N and S as shown. The same is thendone with respect to terminals 24:, except that the direction of currentthrough coil 21 is to be such that magnet 18 will have the relativepositions of its poles N and S as shown.

The previously referred to calibration of scale I 35 may be carried outas follows: A surge current of known maximum value is sent throughconductor 25, and knob 33 is turned anti-clockwise and then slowlyturned clockwise until armature 29 falls away from the ends of strip 16as previously described. The known maximum value of current is thenmarked on scale 35 to register with the indication of pointer 34. Strip16 is then demagnetized, as previously described, another surge currentof a different known maximum value is sent through conductor 25, theabove test with knob 33 repeated, and the known maximum value of thesecond surge current marked on scale 35 to register with the secondposition of pointer 34. This process is repeated until the entire scale35 is suitably calibrated.

The commercial value of my instrument will be evident from the followingexample. Assume that an electric power company operating a longtransmission line supported by many towers wishes to determine which setof line insulators on any one or more of the towers had been flashedover by a lightning discharge or a switching operation, and also wishesto determine the direction and maximum value of the surge current duringthe flashover. This may be accomplished by removingconductor 25 from theinstrument and placing such an instrument on each tower arm in such amanner that a portion of the arm passes through the instrument in placeof conductor 25. To simplify the description, I will assume thatconductor 25 represents a portion of such a tower arm high above theground, and through which the surge current flows when the insulatorssuspended ever,the patrolman sees either armature 38 or 41 of anyinstrument, then he stops, climbs the tower, measures the maximum valueof the surge currentas described, notes and records on his report sheetthe number of the tower, the line conductor suspended from the tower armassociated with the instrument, the direction of the surge, and themaximum value of the surge current. The patrolman then demagnetizesstrip 16 and magnets 17 and l8, remagnetizes magnets 17 and 18, and thenpushes whichever armature is projecting through the casing back into itsplace against the ends of its magnet, all as previously described. Sincea relatively small number of insulators will be flashed over during anyone lightning storm, and since the patrolman has, to climb only thosetowers and to record the indications of only those instruments whichsurround a portion of a tower arm through which a current surge haspassed, it is possible for the patrolman to conduct the tour in theminimum amount of time and in the most economical manner.

If my instrument is installed in such a place hat it is within closevision of an operator, as, for

example, when it is installed on the switchboard of a power house forindicating and measuring the flow of a surge current through somestation conductor, then cover 11 may be omitted, because the operatorcan readily see the positions in which armatures 38 and 41 are withoutmaking them invisible in one of their positions.

Inaccordance with the provisions of the patent statutes, I havedescribed the principles of operation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof,but I desire to have it understood that the apparatus shown anddescribed is only illustrative and that the invention may be carried outby other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An instrument for measuring the maximum value of an electric currentsurge that flowed through a conducting body, said instrument comprisinga strip of magnetic material possessing a high degree of magneticretentivity and being adapted to be so positioned adjacent theconducting body that the magnetic flux surrounding the latter during acurrent surge therethrough magnetizes the strip, a magnetic armaturemovable from one to the other of two positions, one of said positionsbeing its attracted position when said strip is magnetized, saidarmature being biased to move towards its second position, whereas saidstrip has suificient magnetic force to hold the armature in itsattracted position after a current surge has flowed through theconducting body, means for exerting on said armature an opposing forceof sufiicient magnitude to overcome the magnetic force holding it in itsattracted position after a surge has occurred, and means for indicatingin terms of surge current the magnitude of the opposing force exerted onsaid armature.

2. An instrument for measuring the maximum value of an electric currentsurge that flowed through a conducting body, said instrument comprisinga curved strip of magnetic material possessing a high degree of magneticretentivity and having two spaced apart ends, said strip being adaptedto be so positioned around the conducting body that the magnetic fluxsurrounding the latter during a current surge therethrough magnetizesthe strip with magnetic poles of opposite polarities at its two ends, amovable magnetic armature so mounted that it can simultaneously engageboth ends of said strip and can move towards and from these ends, saidarmature being biased to move to a position away from the ends of saidstrip, whereas said strip has suflicient magnetic force to hold thearmature in engagement with both ends of the strip after a current surgehas flowed through the conducting body, means for exerting on saidarmature an opposing force of sufiicient magnitude to overcome themagnetic force holding it in engagement with both ends of said stripafter a surge has occurred, and means for indicating in terms of surgecurrent the magnitude of the opposing force exerted on said armature.

3. An instrument for measuring the maximum value of an electric currentsurge that flowed through a conducting body, said instrument comprisinga curved substantially unmagnetized strip of magnetic materialpossessing a high degree of magnetic retentivity and having two spacedapart ends, said strip being adapted to be so positioned around theconducting body that the magnetic flux surrounding the latter during acurrent surge therethrough magnetizes the strip with magnetic poles ofopposite polarities at its two ends, a pivotally mounted substantiallynon-polarized magnetic armature so mounted that it can simultaneouslyengage both ends of said strip and can move towards and from these ends,said armature being biased to move to a position away from the ends ofsaid strip, whereas said strip has sufficient magnetic force to hold thearmature in engagement with both ends of the strip after a current surgehas flowed through the conducting body,

means for exerting on said armature an opposing force of sufiicientmagnitude to overcome the magnetic force holding it in engagement withboth ends of said strip after a surge has occurred, and means forindicating in terms of surge current the magnitude of the opposing forceexerted on said armature.

4. An instrument for measuring the maximum value of an electric currentsurge that flowed through a conductor, said instrument comprising acasing through which the conductor can extend, a strip of magneticmaterial possessing a high degree of magnetic retentivity, said stripbeing so mounted within said casing that the magnetic flux surroundingthe conductor during a current surge therethrough magnetizes the strip,a magnetic armature within said casing movable from one to the other oftwo positions, one of said positions being its attracted position whensaid strip is magnetized, said armature being biased to move towards itssecond position, whereas said strip has sufiicient magnetic force tohold the armature in its attracted position after a current surge hasflowed through the conductor, a spring for exerting on said armature aforce in opposition to the magnetic force holding it in its attractedposition after a surge has occurred, means extending through said casingfor adjusting the force exerted by said spring on said armature, andindicating means secured to said adjusting means and to the outside ofsaid casing for indicating in terms of surge current the force exertedby said spring in overcoming the magnetic force of said strip.

FRANCIS B. MENGER.

